threads / patch / 44405

patchsha1_name: make wraparound of the index into ring-buffer explicit

Subject: [PATCH] sha1_name: make wraparound of the index into ring-buffer explicit

## tl;dr

2 messages between Nov 1, 2016 and Nov 1, 2016. Diffs are folded; open one to read it.

replies: 1people: 2as markdown or json

René Scharfe· Nov 1, 2016, 08:49 UTC · lore

Overflow is defined for unsigned integers, but not for signed ones. Wrap around explicitly for the new ring-buffer in find_unique_abbrev() as we did in bb84735c for the ones in sha1_to_hex() and get_pathname(), thus avoiding signed overflows and getting rid of the magic number 3.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 sha1_name.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Show changes to sha1_name.c +2 −1

diff --git a/sha1_name.c b/sha1_name.c
index 06409a3..73a915f 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -510,7 +510,8 @@ const char *find_unique_abbrev(const unsigned char *sha1, int len)
 {
 	static int bufno;
 	static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
-	char *hex = hexbuffer[3 & ++bufno];
+	char *hex = hexbuffer[bufno];
+	bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);
 	find_unique_abbrev_r(hex, sha1, len);
 	return hex;
 }

-- 
2.10.2

Jeff King· Nov 1, 2016, 15:04 UTC · re: René Scharfe · lore

Re: [PATCH] sha1_name: make wraparound of the index into ring-buffer explicit

On Tue, Nov 01, 2016 at 09:49:07AM +0100, René Scharfe wrote:

> Overflow is defined for unsigned integers, but not for signed ones.
> Wrap around explicitly for the new ring-buffer in find_unique_abbrev()
> as we did in bb84735c for the ones in sha1_to_hex() and get_pathname(),
> thus avoiding signed overflows and getting rid of the magic number 3.

Thanks. I didn't mean to make you do this, but my procrastination won again.

Show 11 quoted lines

> diff --git a/sha1_name.c b/sha1_name.c
> index 06409a3..73a915f 100644
> --- a/sha1_name.c
> +++ b/sha1_name.c
> @@ -510,7 +510,8 @@ const char *find_unique_abbrev(const unsigned char *sha1, int len)
>  {
>  	static int bufno;
>  	static char hexbuffer[4][GIT_SHA1_HEXSZ + 1];
> -	char *hex = hexbuffer[3 & ++bufno];
> +	char *hex = hexbuffer[bufno];
> +	bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer);

Code looks obviously correct (and it even does the "start at 0" thing).

-Peff